Conventionally, in a patent literature 1, a semiconductor device has been proposed that includes a high electron mobility transistor (hereinafter, referred to as HEMT), which is a field-effect transistor, as a horizontal switching device having a hetero-junction structure.
This kind of semiconductor device includes a horizontal HEMT having a hetero-junction structure of GaN and AlGaN. Specifically, the semiconductor device includes a GaN-type semiconductor layer in which a GaN electron transit layer and an AlGaN electron donor layer are stacked on a substrate in order. The AlGaN electron donor layer has a recess at which a thickness is thinned. The semiconductor device includes a gate electrode in the recess. The semiconductor device includes a source electrode and a drain electrode on the AlGaN electron donor layer and the gate electrode is sandwiched between the source electrode and the drain electrode. The recess is provided at a gate implant portion and an outer side of the gate implant portion. The recess includes a first recess between the gate implant portion and the source electrode and a second recess between the gate implant portion and the drain electrode.
In the HEMT, below the AlGaN electron donor layer positioned at both sides of the gate electrode, carriers of 2-dimensional electron gas (hereinafter, referred to as 2DEG) are induced by piezoelectric effect and intrinsic polarization effect. As such, the HEMT generates a current between the source and the drain through the 2DEG carriers and a channel formed at a surface layer portion of the GaN electron transit layer positioned below the gate electrode.
In the HEMT, the part of the AlGaN electron donor layer is thinned by the recess. In the part of the AlGaN electron donor layer having the recess, a stress is eased than the other thicker part. Therefore, in the AlGaN electron donor layer having the recess, an occurrence of the piezoelectric polarization is restricted and a concentration of the 2DEG (hereinafter, referred to as Ns) is reduced. Accordingly, in the AlGaN electron donor layer having the recess, decrease of a breakdown voltage is restricted. Also, when the AlGaN electron donor layer is partially thinned at multiple positions, the maximum electrical field intensity is further reduced.